Teleogenetic controls on fluid flow, rock-water interaction and calcite cementation in Permian rocks of the Delaware Basin, west Texas and southeast New Mexico.

Abstract

Multiple phases of teleogenetic vein calcite are recognized in Guadalupian carbonate shelf, forereef and basinal clastic rocks. Vein cross-cutting relations, kinematic indicators, and stable isotope/gas inclusion data indicate changes in fracture-controlled fluid flow pathways, thermal regime, and chemistry of diagenetic fluids as uplift, exhumation, and meteoric flushing of the basin progressed through time. Early cements associated with contraction faults and crack-seal veins inherited their $\delta\sp{13}$C and $\delta\sp{18}$O signature from Laramide (compression-related) pressure solution of Permian host rock. Progressive lowering of early vein cement $\gamma\sp{18}$O signatures ($-10\perthous$ to $-19.6\perthous$), reflect increased heat flow during episodes of Oligocene volcanism. Intermediate vein calcite generations related to veins reactivated during Basin and Range extension, have relatively constant $\delta\sp{18}$O values ($-7$ to $-8\perthous$), that are compatible with equilibrium with present-day meteoric water. Cement $\delta\sp{13}$C values ($-10$ to $-40\perthous$), are the same as those of secondary calcite associated with overlying Ochoan evaporite dissolution-collapse structures that are by-products of biogenic sulfate reduction. Late vein calcite generations (mean isotopic composition of $-7\perthous\ \delta\sp{18}$O and $-5\perthous\ \delta\sp{13}$C), include scalahedral spars overlain by a variety of speleothem calcite and likely represent a transition from shallow meteoric phreatic to aerated vadose conditions in exhumed basin margin rocks. Striking spatial correlations between regional joints and fractures, Landsat TM geomorphic lineaments, subsurface Ochoan salt dissolution phenomena; variations in formation water geochemistry; sites of Ochoan biogenic native sulfur/secondary calcite mineralization and Guadalupian vein calcite occurrences suggest that fracture systems provided conduits for the convective exchange of fluids both laterally and vertically in the basin. Observations that many of the vein calcite phases are petrographically and isotopically similar to cements more commonly attributed to burial diagenesis indicates the effects of uplift-related water-rock interaction in many basins could be misinterpreted or simply go unrecognized without careful integration of stratigraphic, structural, petrologic and geochemical data.